从locals（）或globals（）中查找并删除Python对象

Question

I'm using telnetlib to communicate with some equipment which has Telnet implemented as single user. Therefore, I have to detect and remove the telnet object created from a previous attempt to establish communication.(Ex: tn = telnetlib.Telnet(HOST) ) My attempt is something like bellow but it does not work:

 if 'tn' in loccals() or 'tn' in globals():
     print "Telnet object exists. Remove it."
     tn.close()
     del tn
 else:
     print "Create a Telnet object."
     global tn
     tn = telnetlib.Telnet(HOST)

print tn

Answer 1

Don't delete, rebind. Start with tn set to None :

tn = None

Now you can test for the value:

if tn is not None:
    tn.close()
    tn = None
else:
    tn = telnetlib.Telnet(HOST)

Note that the global keyword marks a name as global in the whole scope , not just from that line onwards.